Several recent threads have led me to believe that we need to review how natural tip lead occurs. Like most things in skiing coaching and instruction we work in cycles and revisiting the idea of tip lead and foot containment seems to be occurring lately. Here is some food for though and a chance for us here at Epic to offer a comprehensive overview of tip lead and why it occurs.
In the most basic form tip lead is a result of movements commonly called upper lower body separation and independent leg steering. While there are countless variations on this theme a developing skier must pass through a stage where they explore learning to turn the legs in the hip sockets while maintaining a rotationally stable pelvis and torso. In the beginning stages of a skier's development Barnes' bar stool exercise is a good example of this because it features isolated hip movements where the entire leg moves as a unit while the pelvis and torso remains facing forward. The net result is the feet stay hip width apart and directly below each hip and any lead that occurs is the direct result of the pelvis and the feet facing different directions. Obviously the greater the difference in direction between the pelvis and feet, the more tip lead will occur. The limiting factor here is that the pivot point in the hips are actually in the center of the femoral heads which are usually less than a foot apart. When we consider the rotational range of motion in the hip joint varies from individual to individual we can only offer an approximation of what is normal but somewhere around 100' is about average. So in pivot slips where the skis rotate through 180' some other part of the body must also rotate. The most common body regions we could use would be the lower leg and foot, followed by the low back but when we use the low back, the pelvis turns. Which is generally something we try to avoid during that maneuver, so it sort of becomes a last option after turning the legs and feet. In any event the feet actually remain an equal distance apart in spite of the direction the feet are facing. Lateral separation varies since at the extreme ends of this RoM the feet line up front to back not so much side to side. It's here that the prescribed constant lateral foot to foot width idea mentioned by PSIA breaks down. A good analogy is the windshield wipers on your car because they work very much this way. The pivot points never get any closer, or further away from each other but when not in use the wiper blades line up in an almost end to end way with little to no lateral width between the blades. The extreme end of the rotational RoM in pivot slips produce just such an alignment of the skis and feet.
A second type of tip lead occurs as a function of leg length. Vertical separation changes as one leg gets shorter and as that occurs, the femur of the bending leg moves from perpendicular to the ski, to parallel to the ski. As this happens the entire lower leg moves forward with the knee. In isolation this type of tip lead is where many believe fore / aft balance becomes a really big issue and foot containment becomes a very big focus. If the skis are equally weighted balancing somewhere between the skis is the natural outcome that gets mentioned as why foot pull back on the flexing leg and foot push forward of the outside foot is necessary. Again that is if the feet are equally weighted but as the percentage of foot to foot weight changes the balance point shifts towards the foot doing most of the weight bearing. At one extreme 100% weight on one foot means the other ski isn't even on the snow and balance is solely on that one foot. So it's rather irrelevant if that ski is far ahead of the other, and considering how the leg flexes in the first place it is unlikely that foot will drop aft. But here is where advanced skiers can over do the idea of foot containment and as they attempt to pull the foot back / push the outside foot forward. They are also likely to turn the pelvis along with moving the foot, or they end up using whole body rotary which moves the entire half of the body with the foot they moved. USSA prescribes a square to the skis stance through the transition which means the entire body is facing the same direction. This sounds suspiciously like promoting whole body rotary but in reality their top stars do not strictly follow that "rule" any more than the top PSIA coaches follow the prescribed counter rotated stance through the transition idea. Mechanically I would say foot elevation needs to be considered when we do a traverse and we need to accommodate the unequal leg length that will naturally occur due to the different foot elevations. As we allow our body to cross over the skis and into the new turn, the leg length becomes equal for a split second as the skis become flat to the snow but exactly where the skis get flat is another issue open to debate. I see merit in both ideas and knowing how to get the skis flat early and a bit later gives us options, which I feel is always a good idea.
So how does this effect how we approach managing tip lead? Well it is somewhat dependent on the situation and the skier's ability level, at lower levels large leg length differences are less common and the rotary type of tip lead is more common. So their foot / tip lead management would consist of mostly of maintaining the BoS / CoM alignments in that narrower window where the feet move beneath the hips, hips move over the feet and both move relative to each other. More advanced skiers tend to use a wider RoM in the lateral realm, which forces the feet to move forward and backwards more because of the relative position of the femur to the slope. Minimizing the amount of tip lead and drawing the feet back beneath the body allows them to perform a weight transfer much earlier because the dynamic nature of the turns means their greater forward momentum working against the new edge platform causes the skis to turn sooner and the ski to bend more thanks to the return forces coming back up from the snowpack.
Of course all of this is snow dependent in the sense that firm snow and ice deforms very little when we press down on it. It has morphed into a very cohesive and almost solid layer that can easily support our weight. Soft snow lacks the cohesiveness of ice and like a ball room that kids play in, we sink into the snow until it compresses enough to support us. It feels like we are floating and skimming through the snow rather than standing on it like we are on solid ground. That shearing away age hardens it though and with enough skier traffic powder morphs into a more consolidated layer. Not to mention the snow is morphing all on it's own and over time will form strong bridges between snow particles. Which is why dry "Colorado" snow avalanche so easily when compared to wetter snow elsewhere. I know this may seem unrelated to ski turns but snow conditions in different parts of the country are responsible for most of the technique variations we see in different sections of organizations like PSIA and it's counterparts around the world. I see it here at Epic as well, when some final form gets offered as the only way to ski.
I am sure this post will lead to some debate as well and I welcome that as long as we avoid the my way is the only way posts.